You are correct 830 uses about 0.38 W at Idle, the M4 is 0.28 higher Watts at Idle.
However at reads/and writes can be up to almost 2 Watts Higher. Would not take much time reading/writting to overcome the slight diff at idle.
In most of the "final word" This has been Anadtechs recommendation 830 for desktop and m4 for laptop.
As to performance diff. There is almost NO noticable diff between m4 AND 830 in day-to-day real life usage.
Have both 2 128 gig M4s and one 256 gig M4 Plus 2 128 gig 830s and one 256 gig 830.
The pextor M3 would probably be a even better choice in terms of battery life, But generall the plextor is higher priced.http://www.anandtech.com/show/5851/plextor-m3-pro-256gb-review/9